The present invention relates to the processing of images of the subsurface and especially to the transformation of seismic images into chrono-stratigraphic representations.
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. Furthermore, all embodiments are not necessarily intended to solve all or even any of the problems brought forward in this section.
It is known, especially in oil exploration, to determine the position of oil reservoirs from the results of geophysical measurements carried out from the surface or in well bores. According to the technology of reflection seismology, these measurements involve emitting a wave (acoustic waves or electromagnetic radiation) into the subsurface and measuring a signal comprising a plurality of echoes of the wave on geological structures being investigated. These structures are typically surfaces separating distinct materials, faults, etc. Other measurements are carried out from wells.
Chrono-stratigraphic analysis (sequence stratigraphic analysis) is very important to understand basin evolution, predict the sedimentary facies distribution for both petroleum exploration and development. This analysis is based on the fundamental assumption that seismic reflectors are surfaces of chrono-stratigraphic significance. This assumption implies that an individual seismic reflector is a “time-line” through a depositional basin that represents a surface of the same geologic age. Faults are excluded from this definition.
A seismic cross section is formed by the juxtaposition in a plane of sampled one-dimensional signals referred to as seismic traces (2D). Likewise, a seismic block is formed by the juxtaposition of seismic traces in a volume (3D seismic image). The expression “seismic image” refers either to a seismic cross section or a seismic block.
In a seismic image, the luminous intensity of a pixel is proportional to the seismic magnitude represented by one-dimensional signals.
Computing a chrono-stratigraphic representation of a seismic image often requires, in regard of the previous methods, the synthesis of seismic horizons in the cross section or the block.
Several methods have been devised for carrying out syntheses of horizons. For instance, the thesis by Marc Donias, submitted on Jan. 28, 1999 to the University of Bordeaux 1 and entitled “Caractérisation de champs d'orientation par analyse en composantes principales et estimation de la courbure. Application aux images sismiques, [Characterization of orientation fields by principal components analysis and estimation of curvature. Application to seismic images]”, describes in detail possible schemes for carrying out horizon synthesis. The U.S. Pat. No. 6,771,800 B1 also describes a possible method to create chrono-stratigraphic interpretation of a seismic image.
Such methods have drawbacks especially if the resolution of the seismic image is very low or contains a high noise level. In such case, computed horizons of the seismic images may be erroneous and thus may provide inadequate results. In addition, these methods may be erroneous if the assumption that seismic reflectors are surfaces of chrono-stratigraphic significance is false.
There is thus a need for improving the computation chrono-stratigraphic representation in such cases.